/* * Copyright (C) 2011 The Guava Authors * * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except * in compliance with the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software distributed under the License * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express * or implied. See the License for the specific language governing permissions and limitations under * the License. */ package com.google.common.hash; import java.nio.charset.Charset; import com.google.common.annotations.Beta; /** * A {@link PrimitiveSink} that can compute a hash code after reading the input. * Each hasher should translate all multibyte values ({@link #putInt(int)}, * {@link #putLong(long)}, etc) to bytes in little-endian order. * *

* Warning: The result of calling any methods after calling {@link #hash} * is undefined. * *

* Warning: Using a specific character encoding when hashing a * {@link CharSequence} with {@link #putString(CharSequence, Charset)} is * generally only useful for cross-language compatibility (otherwise prefer * {@link #putUnencodedChars}). However, the character encodings must be * identical across languages. Also beware that {@link Charset} definitions may * occasionally change between Java releases. * *

* Warning: Chunks of data that are put into the {@link Hasher} are not * delimited. The resulting {@link HashCode} is dependent only on the bytes * inserted, and the order in which they were inserted, not how those bytes were * chunked into discrete put() operations. For example, the following three * expressions all generate colliding hash codes: * *

 *    {@code
 *
 *   newHasher().putByte(b1).putByte(b2).putByte(b3).hash()
 *   newHasher().putByte(b1).putBytes(new byte[] { b2, b3 }).hash()
 *   newHasher().putBytes(new byte[] { b1, b2, b3 }).hash()}
 * 
* *

* If you wish to avoid this, you should either prepend or append the size of * each chunk. Keep in mind that when dealing with char sequences, the encoded * form of two concatenated char sequences is not equivalent to the * concatenation of their encoded form. Therefore, * {@link #putString(CharSequence, Charset)} should only be used consistently * with complete sequences and not broken into chunks. * * @author Kevin Bourrillion * @since 11.0 */ @Beta public interface Hasher extends PrimitiveSink { @Override Hasher putByte(byte b); @Override Hasher putBytes(byte[] bytes); @Override Hasher putBytes(byte[] bytes, int off, int len); @Override Hasher putShort(short s); @Override Hasher putInt(int i); @Override Hasher putLong(long l); /** * Equivalent to {@code putInt(Float.floatToRawIntBits(f))}. */ @Override Hasher putFloat(float f); /** * Equivalent to {@code putLong(Double.doubleToRawLongBits(d))}. */ @Override Hasher putDouble(double d); /** * Equivalent to {@code putByte(b ? (byte) 1 : (byte) 0)}. */ @Override Hasher putBoolean(boolean b); @Override Hasher putChar(char c); /** * Equivalent to processing each {@code char} value in the {@code CharSequence}, * in order. The input must not be updated while this method is in progress. * * @since 15.0 (since 11.0 as putString(CharSequence)). */ @Override Hasher putUnencodedChars(CharSequence charSequence); /** * Equivalent to {@code putBytes(charSequence.toString().getBytes(charset))}. */ @Override Hasher putString(CharSequence charSequence, Charset charset); /** * A simple convenience for {@code funnel.funnel(object, this)}. */ Hasher putObject(T instance, Funnel funnel); /** * Computes a hash code based on the data that have been provided to this * hasher. The result is unspecified if this method is called more than once on * the same instance. */ HashCode hash(); }